OCR Text |
Show above the ( normal norinal ) water ( m J43 ) surface indicates that such deposits could ( have liave ) been laid down only during the most extreme floods . All ordinary floods cut these banks rather than add to their height . It seems evident , therefore , that these enormous flats or , in reality , bars , many of which contain from 1 to 5 million cubic yards , are the result of extreme floods and that except for side cutting and surface erosion they are fairly permanent for long periods of time . Their presence may also be explained as a result of a change in flow conditions resulting from changes in climate . In the canyon sections we therefore have three degrees of permanency : First , the bed of the ( low-flow lowflow ) channel of which the crossing bars are a part which , to speak ( accu- accu ) rately , is constantly shifting as the result of a ( rear- rear ) rangement of the finer materials of which it is made up and of the constant addition of material brought into the section both in suspension and as bed load . Second , the sand bars which lie from 1 to 5 feet above the water at ( low-flow lowflow ) stages and which are fairly permanent for periods between ordinary ( high- high ) water stages . Such minor changes as take place . consist of the gradual cutting and sloughing off along the edges and changes in surface ( configura configura- configura ) tion due to wind . Third , the large ( willow-covered willowcovered ) flats which are . permanent for long periods between exceptionally high floods except for spasmodic cutting along ( their their- their ) edges during ordinary flood periods and by ( surface surfaced ) erosion . |